U.S. patent application number 13/769659 was filed with the patent office on 2013-06-20 for charge acceptance limit determination apparatus and charge acceptance limit determination method.
This patent application is currently assigned to FURUKAWA AUTOMOTIVE SYSTEMS INC.. The applicant listed for this patent is Furukawa Automotive Systems Inc., Furukawa Electric Co., Ltd.. Invention is credited to Shinichi NOMOTO.
Application Number | 20130154574 13/769659 |
Document ID | / |
Family ID | 45873896 |
Filed Date | 2013-06-20 |
United States Patent
Application |
20130154574 |
Kind Code |
A1 |
NOMOTO; Shinichi |
June 20, 2013 |
Charge Acceptance Limit Determination Apparatus and Charge
Acceptance Limit Determination Method
Abstract
A charge acceptance limit determination apparatus includes a
voltage measuring unit that measures a voltage of a secondary
battery, a current measuring unit that measures an electric current
flowing through the secondary battery, and a determining unit that
determines whether or not the secondary battery has reached a
charge acceptance limit in accordance with a position on a
current-voltage plane of a voltage value and a current value that
are measured by the voltage measuring unit and the current
measuring unit.
Inventors: |
NOMOTO; Shinichi; (Tokyo,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Furukawa Electric Co., Ltd.;
Furukawa Automotive Systems Inc.; |
Tokyo
Shiga |
|
JP
JP |
|
|
Assignee: |
FURUKAWA AUTOMOTIVE SYSTEMS
INC.
Shiga
JP
FURUKAWA ELECTRIC CO., LTD.
Tokyo
JP
|
Family ID: |
45873896 |
Appl. No.: |
13/769659 |
Filed: |
February 18, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
PCT/JP2011/071438 |
Sep 21, 2011 |
|
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13769659 |
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Current U.S.
Class: |
320/148 |
Current CPC
Class: |
Y02E 60/10 20130101;
H01M 10/48 20130101; H02J 7/0047 20130101; G01R 31/3842 20190101;
G01R 31/392 20190101; H02J 7/0048 20200101; G01R 31/389 20190101;
H02J 7/00 20130101; G01R 31/367 20190101 |
Class at
Publication: |
320/148 |
International
Class: |
H02J 7/00 20060101
H02J007/00 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 24, 2010 |
JP |
2010213842 |
Claims
1. A charge acceptance limit determination apparatus comprising: a
voltage measuring unit that measures a voltage of a secondary
battery; a current measuring unit that measures an electric current
flowing through the secondary battery; and a determining unit that
determines whether or not the secondary battery has reached a
charge acceptance limit in accordance with a position on a
current-voltage plane of a voltage value and a current value that
are measured by the voltage measuring unit and the current
measuring unit.
2. The charge acceptance limit determination apparatus according to
claim 1, wherein the determining unit determines whether or not the
secondary battery has reached a charge acceptance limit based on a
distance of a position corresponding to the voltage value and the
current value from a predetermined base point on the
current-voltage plane.
3. The charge acceptance limit determination apparatus according to
claim 1, wherein the determining unit obtains, on the
current-voltage plane, a midpoint between a position corresponding
to the voltage value and the current value that are newly measured
and a position corresponding to the voltage value and the current
value that have been previously measured, and determines whether or
not the secondary battery has reached a charge acceptance limit
based on a distance of the midpoint from a predetermined base
point.
4. The charge acceptance limit determination apparatus according to
claim 3, wherein the determining unit determines whether or not the
secondary battery has reached a charge acceptance limit based on a
distance of the predetermined base point from a midpoint between
the previously obtained midpoint and the newly obtained
midpoint.
5. The charge acceptance limit determination apparatus according to
claim 2, wherein, when the distance is smaller than a predetermined
threshold, the determining unit determines that the secondary
battery has reached a charge acceptance limit.
6. The charge acceptance limit determination apparatus according to
claim 2, wherein, when a weighted average of the distances is
smaller than a predetermined threshold, the determining unit
determines that the secondary battery has reached a charge
acceptance limit.
7. The charge acceptance limit determination apparatus according to
claim 2, wherein the base point is reset depending on degradation
of the secondary battery.
8. The charge acceptance limit determination apparatus according to
claim 1, wherein the determining unit has a reference value of a
voltage value and a reference value of a current value and, when at
least one of a measured voltage value and a measured current value
is less than or equal to these reference values, the relevant
measured value is excluded from a target of the determination.
9. The charge acceptance limit determination apparatus according to
claim 1, wherein the determining unit has a proper range for a
voltage value and a proper range for a current value, and when one
of a measured voltage value and a measured current value is out of
the proper ranges, the relevant measured value is corrected to a
predetermined specified value.
10. The charge acceptance limit determination apparatus according
to claim 1, comprising: a calculating unit that calculates an SOC
indicating a state of charge of the secondary battery, wherein an
SOC calculated by the calculation unit when the determining means
has determined that the charge acceptance limit has reached is
taken as a charge acceptance limit SOC.
11. The charge acceptance limit determination apparatus according
to claim 10, wherein, after the charge acceptance limit SOC has
been set, when an SOC having a value greater than the charge
acceptance limit SOC has been calculated by the calculating unit,
the charge acceptance limit SOC is updated with the relevant
SOC.
12. A charge acceptance limit determination method comprising:
measuring a voltage of a secondary battery to obtain a voltage
value; measuring an electric current flowing through the secondary
battery to obtain a current value; determining whether or not the
secondary battery has reached a charge acceptance limit in
accordance with a position on a current-voltage plane of the
voltage value and the current value.
13. The method according to claim 12 wherein said determining
whether or not the secondary battery has reached a charge
acceptance limit in accordance with a position on a current-voltage
plane of the voltage value and the current value is performed by a
processor in cooperation with a memory.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This is a continuation application of International Patent
Application No. PCT/JP2011/071438, filed Sep. 21, 2011, which
claims the benefit of Japanese Patent Application No. 2010-213842
filed Sep. 24, 2010, the contents of both of which are incorporated
by reference herein in its entirety.
BACKGROUND OF INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a charge acceptance limit
determination apparatus and a charge acceptance limit determination
method.
[0004] 2. Background of the Invention
[0005] Japanese Laid-Open Patent Publication No. 2001-16800
discloses a technique of preventing unnecessary power generation by
controlling power generation of an alternator based on a state of
charge (SOC) of a secondary battery.
[0006] According to the aforementioned control based on the SOC,
the control is generally performed in such a manner that the SOC,
which is being measured, falls in a predetermined range between
SOC2 and SOC1, as shown in FIG. 11. However, it is known that, when
a full charge state of a secondary battery when new is defined as
SOC=100%, the SOC thus defined changes with an elapse of time (a
value decreases). That is to say, as shown in FIG. 12A, an SOC at
an upper chargeable limit of the secondary battery, i.e., a charge
acceptance limit SOC, decreases as the secondary battery degrades.
FIGS. 12A to 12C are diagrams showing aging of the charge
acceptance limit SOC of the secondary battery. In these drawings,
references numerals 51 and 52 indicate the charge acceptance limit
SOC and a chargeable charge control range, respectively.
[0007] A decrease in the charge acceptance limit SOC is caused by
sulfation (crystals of sulfate) which is built up on electrode
plates of the battery and which does not dissolve by being hardened
during a long time of use. As the sulfation which does not dissolve
increases on the electrode plates, an area of charge/discharge on
the electrode plates decreases and leads to a decrease in the
charge acceptance limit SOC.
[0008] When the charge acceptance limit SOC decreases as shown in
FIG. 12A, the secondary battery cannot be charged to an upper limit
SOC1 of a charge control range set in advance, and a charge
acceptance limit SOC 51 which is lower than that will become an
upper chargeable limit. As a result, the charge control range 52
will be greater than or equal to the lower limit SOC2 and less than
or equal to the charge acceptance limit SOC 51, and thus the
controllable range becomes narrower.
[0009] As the degradation of the secondary battery further
progresses, as shown in FIG. 12B, the charge acceptance limit SOC
51 becomes lower than the lower limit SOC2 of the charge control
range. In such a state, the charge control range cannot be ensured
and the charging of the secondary battery will be always carried
out. As a result, fuel consumption of the engine cannot be
improved. In order to ensure the charging control range and to
carry out charging control even in a state where degradation of the
secondary battery has progressed, it is necessary to detect the
charge acceptance limit SOC 51 which decreases as the degradation
progresses and, based on this, to appropriately adjust the charge
control range as shown in FIG. 12C.
[0010] The present invention has been contrived to solve the
aforementioned problem and an object of the present invention is to
provide a charge acceptance limit determination apparatus and a
charge acceptance limit determination method for a secondary
battery capable of accurately determining the charge acceptance
limit of the secondary battery.
SUMMARY OF INVENTION
[0011] A charge acceptance limit determination apparatus of an
aspect of the invention includes a voltage measuring unit that
measures a voltage of a secondary battery, a current measuring unit
that measures an electric current flowing through the secondary
battery, and a determining unit that determines whether or not the
secondary battery has reached a charge acceptance limit in
accordance with a position on a current-voltage plane of a voltage
value and a current value that are measured by the voltage
measuring unit and the current measuring unit.
[0012] With such a configuration, a charge acceptance limit of the
secondary battery can be determined accurately.
[0013] According to another aspect, in addition to the above
aspect, the determining unit determines whether or not the
secondary battery has reached a charge acceptance limit based on a
distance of a position corresponding to the voltage value and the
current value from a predetermined base point on the
current-voltage plane.
[0014] With such a configuration, it is possible to make an easy
adjustment to a change in the environment or the like by moving the
base point.
[0015] According to yet another aspect, in addition to the above
aspect, the determining unit obtains, on the current-voltage plane,
a midpoint between a position corresponding to the voltage value
and the current value that are newly measured and a position
corresponding to the voltage value and the current value that have
been previously measured, and determines whether or not the
secondary battery has reached a charge acceptance limit based on a
distance of the midpoint from a predetermined base point.
[0016] With such a configuration, even in a case where the voltage
value and the current value vary, the charge acceptance limit can
be determined accurately by suppressing the variation.
[0017] According to still another aspect, in addition to the above
aspect, the determining unit determines whether or not the
secondary battery has reached a charge acceptance limit based on a
distance of the predetermined base point from a midpoint between
the previously obtained midpoint and the newly obtained
midpoint.
[0018] With such a configuration, even in a case where there is a
large variation in the voltage value and the current value, the
charge acceptance limit can be determined accurately by suppressing
the variation.
[0019] According to still another aspect, in addition to the above
aspect, when the distance is smaller than a predetermined
threshold, the determining unit determines that the secondary
battery has reached a charge acceptance limit.
[0020] With such a configuration, by comparing with the threshold,
the charge acceptance limit can be obtained in a facilitated
manner.
[0021] According to still another aspect, in addition to the above
aspect, when a weighted average of the distances is smaller than a
predetermined threshold, the determining unit determines that the
secondary battery has reached a charge acceptance limit.
[0022] With such a configuration, by using a weighted average, the
charge acceptance limit can be determined in a simple and accurate
manner.
[0023] According to still another aspect, in addition to the above
aspect, the base point is reset depending on degradation of the
secondary battery.
[0024] With such a configuration, by resetting of the base point, a
simplified handling can be achieved even in a case where the
secondary battery has degraded.
[0025] According to still another aspect, in addition to the above
aspect, the determining unit has a reference value of a voltage
value and a reference value of a current value and, when at least
one of a measured voltage value and a measured current value is
less than or equal to these reference values, the relevant
measurement value is excluded from a target of the
determination.
[0026] With such a configuration, the charge acceptance limit can
be determined more accurately by excluding an irregular measurement
value when such an irregular measurement value is obtained.
[0027] According to still another aspect, in addition to the above
aspect, the determining unit has a proper range for a voltage value
and a proper range for a current value, and when one of a measured
voltage value and a measured current value is out of the proper
ranges, the relevant measured value is corrected to a predetermined
specified value.
[0028] With such a configuration, the charge acceptance limit can
be determined more accurately by correcting an irregular measured
value to a specified value when such irregular measured value was
obtained.
[0029] According to still another aspect, in addition to the above
aspect, the invention includes a calculating unit that calculates
an SOC indicating a state of charge of the secondary battery, and
an SOC calculated by the calculation unit when the determining
means has determined that the charge acceptance limit has reached
is taken as a charge acceptance limit SOC.
[0030] With such a configuration, for example, the charge
controlling can be performed appropriately, since the charge
acceptance limit SOC can be obtained.
[0031] According to still another aspect, in addition to the above
aspect, after the charge acceptance limit SOC has been set, when an
SOC having a value greater than the charge acceptance limit SOC has
been calculated by the calculating unit, the charge acceptance
limit SOC is updated with the relevant SOC.
[0032] With such a configuration, the charge acceptance limit SOC
can be corrected even in a case where the charge acceptance limit
SOC was falsely set.
[0033] Further, a charge acceptance limit determination method of
the invention includes measuring a voltage of a secondary battery
to obtain a voltage value, measuring an electric current flowing
through the secondary battery to obtain a current value, and
determining whether or not the secondary battery has reached a
charge acceptance limit in accordance with a position on a
current-voltage plane of the voltage value and the current
value.
[0034] With such a method, the charge acceptance limit of the
secondary battery can be determined accurately.
[0035] According to an aspect of the invention, a charge acceptance
limit determination apparatus and a charge acceptance limit
determination method can be provided that can accurately determine
a charge acceptance limit of a secondary battery.
[0036] Further features of the present invention will become
apparent from the following detailed description of exemplary
embodiments with reference to the attached drawings.
BRIEF DESCRIPTION OF DRAWINGS
[0037] FIG. 1 is a principle diagram for explaining an operation
principle of the invention.
[0038] FIG. 2 is a diagram for explaining an operation regarding
the principle diagram shown in FIG. 1.
[0039] FIGS. 3A to 3C are diagrams for explaining an operation
regarding the principle diagram shown in FIG. 1.
[0040] FIG. 4 is an illustrative configuration of an embodiment of
the invention.
[0041] FIG. 5 is a diagram for explaining an outline of an
operation of the embodiment shown in FIG. 4.
[0042] FIG. 6 is a flowchart for explaining an operation of the
embodiment shown in FIG. 4.
[0043] FIG. 7 is a diagram for explaining the details of the
voltage excess rate calculation in the flow chart shown in FIG.
6.
[0044] FIGS. 8A to 8C are diagrams showing actual results of the
process shown in FIG. 6.
[0045] FIGS. 9A to 9D are diagrams showing results of actual
measurements according to a variant embodiment.
[0046] FIGS. 10A to 10D are diagrams showing results of actual
measurements according to a variant embodiment.
[0047] FIG. 11 is a graph showing an example of charge control of
the related art.
[0048] FIGS. 12A to 12C are diagrams showing an example of the
charge controlling of the related art.
DETAILED DESCRIPTION
[0049] Hereinafter, embodiments of the present invention will be
described. In the following description, an operation principle of
the present invention will be described with reference to the
principle diagram shown in FIG. 1 and, thereafter, embodiments will
be described.
(A) Explanation of the Principle Diagram
[0050] FIG. 1 is a principle diagram for explaining an operation
principle of the invention. As shown in FIG. 1, the charge
acceptance limit determination apparatus of the present invention
includes a voltage measuring unit 2, a current measuring unit 3 and
a determining unit 4, and determines whether or not a secondary
battery 1 has reached a "charge acceptance limit" which is a limit
that no more charge can be accepted.
[0051] The secondary battery 1 is, for example, comprised of a lead
battery or the like. The voltage measuring unit 2 measures a
terminal voltage of the secondary battery 1 and gives notice to the
determining unit 4. The current measuring unit 3 measures an
electric current (a charging current and a discharging current)
flowing through the secondary battery 1 and gives notice to the
determining unit 4. The determining unit 4 plots, on a
current-voltage plane, a voltage value measured by the voltage
measuring unit 2 and a current value measured by the current
measuring unit 3, and determines whether or not the secondary
battery 1 has reached the charge acceptance limit based on a
position of the plotted point. Herein, "to plot on a
current-voltage plane" not only means to depict a point on an
actual plane, but also means, for example, to virtually depict on a
storage space such as a memory (to determine a position), to
specify data corresponding to any current value and a voltage value
in a storage table (e.g., an array, etc.) in which a predetermine
data can be obtained by specifying any two values, and to determine
values corresponding to the voltage V and the current I in function
f(V, I).
(B) Explanation of Operation of Principle Diagram
[0052] Now, referring to FIG. 2, the operation principle of the
invention will be described. Here, FIG. 2 is a plot of the voltage
and the current on a current-voltage plane for a case where the
charging is performed in a range where the SOC (State of Charge) of
the secondary battery 1 varies from 30% to 100%. In this example,
points plotted in a region 61 correspond to a range where the SOC
is between 30% and 50%, points plotted in a region 62 correspond to
a range where the SOC is between 50% and 80%, points plotted in a
region 63 correspond to a range where the SOC is between 80% and
90%, and points plotted in a region 64 correspond to a range where
the SOC is between 90% and 100%. As can be seen in FIG. 2, as the
SOC becomes greater and approaches the charge acceptance limit,
there is a tendency that the voltage becomes greater than or equal
to 14V and the current becomes less than or equal to 10 A. Also,
the region to be plotted differs depending on the value of the
SOC.
[0053] It is to be noted that there are two definitions for SOC.
First is a definition in which a full charge state of a secondary
battery when new is taken as 100% and the SOC in the full charge
state decreases from 100% depending on the degradation. In such a
case, when degraded, the SOC will not become 100% even when fully
charged. Second is a definition in which a value that only takes an
amount of charging into consideration, and excluding an amount of
degradation, is taken as the SOC. In such a case, irrespective of
the degree of degradation, the fully charged state is always taken
as SOC=100%. Herein, the first definition is used for the SOC.
[0054] FIG. 3A is a diagram in which a voltage of the secondary
battery 1 and an electric current flowing through the secondary
battery 1 in a state near the charge acceptance limit are plotted
on a current-voltage plane. As shown in FIG. 3A, with the secondary
battery 1 near the charge acceptance limit, the density of points
plotted in a range between 14.0 V and 14.5 V and in a range between
-10 A and +10 A is high. In this manner, determination of whether
or not being the charge acceptance limit can be made depending on
where on the current-voltage plane the points are plotted.
[0055] According to the invention, the voltage and the electric
current of the secondary battery 1 measured with the voltage
measuring unit 2 and the current measuring unit 3 are plotted on
the current-voltage plane, and, for example, when the plotted
points are plotted in a region 70 enclosed by a curved line shown
in FIG. 3B with a high frequency, it can be determined as the
charge acceptance limit. In this manner, by making a determination
based on the positions of the points plotted on the current-voltage
plane, the charge acceptance limit can be detected with a high
accuracy. Also, since the voltage and the current of the secondary
battery 1 change continually due to fluctuation of a load connected
thereto or due to fluctuation of the power generator, it is
preferable to make a determination from a statistical point of view
based on the results of a plurality of times of plots to determine
the charge acceptance limit accurately. In other words, among the
plurality of times of plots, it can be determined as being the
charge acceptance limit in a case, for example, when 60% or more is
within a predetermined region.
[0056] In the case of FIG. 3B, the determination is made based on
whether plotted in an elliptical region 70 or not, but since the
determination of whether or not enclosed in the ellipse is
complicated, for example, as shown in FIG. 3D, the determination
can be made by whether or not plotted in a rectangular region 71.
With such a method, a determination process can be simplified,
since whether or not included can be determined by comparison with
threshold values corresponding to four sides.
[0057] In the aforementioned principle diagrams, description was
made by taking an example in which the regions 70 and 71 are fixed,
but it is generally known that the charge acceptance limit SOC
gradually decreases due to aging. Accordingly, the regions 70 and
71 may be moved towards the left hand side in the drawings in
accordance with an elapse of time. Also, rather than plotting on
the current-voltage plane, it is possible to prepare a table in
which the current value and the voltage value are stored in
association with information indicating whether inside or outside
the region, and to determine whether or not it is the charge
acceptance limit based on this table. As a method of dealing with
aging for a case where a table is used, for example, a plurality of
tables corresponding to aging may be prepared and a table
corresponding to an elapse of time can be selected. Alternatively,
it is possible to provide a single table and to retrieve a
corresponding value from the table after having normalized the
current value and the voltage value, and to change a normalization
parameter in accordance with an elapse of time.
(C) Description of Configuration of the Embodiment
[0058] FIG. 4 is a diagram illustrating an exemplary configuration
of a charge acceptance limit determination apparatus of the present
embodiment. As shown in this figure, the charge acceptance limit
determination apparatus 10 of the present invention includes an
operation processing unit 11, a voltage sensor 12, a current sensor
13, a temperature sensor 14, a storage unit 15, a timer 16, and an
I/F (Interface) 17 as its main constituent elements, determines
whether or not the secondary battery 20 has reached the charge
acceptance limit. In an example shown in FIG. 4, a power generator
21 for charging is connected in series to the secondary battery 20
and is connected in parallel to a load 22.
[0059] The operation processing unit 11 executes various operation
processes based on a program 15a and data 15b that are stored in
the storage unit 15. The voltage sensor 12 measures a terminal
voltage of the secondary battery 20 and outputs to the operation
processing unit 11. The current sensor 13 measures a charging
current (an electric current flowing from the power generator 21)
and a discharge current (an electric current flowing to the load
22) of the secondary battery 20 and outputs to the operation
processing unit 11. In the following description, the charging
current is expressed as "positive" and the discharge current is
expressed as "negative".
[0060] The temperature sensor 14 measures a temperature of the
secondary battery 20 itself or its ambient temperature and outputs
to the operation processing unit 11. The storage unit 15 is, for
example, comprised of a semiconductor memory such as a ROM (Read
Only Memory) and a RAM (Random Access Memory) and stores a program
15a and data 15b, and also operates as a working area when the
operation processing unit 11 executes the program 15a. It is to be
noted that the program 15a includes a program for causing the
operation processing unit 11 to execute a process described below.
The data 15b has data necessary for executing the process described
below.
[0061] The timer 16 generates time information and supplies it to
the operation processing unit 11. The I/F 17 converts a data
expression format upon delivering and receiving data to and from an
external device, not shown.
(D) Explanation of Operation of Embodiment
[0062] Next, an operation of an embodiment shown in FIG. 4 will be
described. In the following, first, an overall operation of the
present embodiment will be described with reference to FIG. 5 and
thereafter a detailed operation will be described with reference to
a flow chart of FIG. 6.
[0063] FIG. 5 is a chart for explaining an overall operation of the
present embodiment. In this example, points A to F, which have been
measured in this order, are plotted on a current-voltage plane
indicating an electric current on its vertical axis and a voltage
on its horizontal axis. Also, in this diagram, a base point is
provided on a horizontal axis and proper ranges of the voltage and
the electric current are indicated with broken lines that are
parallel to the horizontal axis and the vertical axis,
respectively.
[0064] First, in a first measurement, point A is plotted at a point
corresponding to the voltage and the electric current measured with
the voltage sensor 12 and the current sensor 13. In the second
measurement, point B is plotted. Then, a midpoint (1) between point
A and point B is obtained and a distance L1 between the midpoint
(1) and the base point is obtained.
[0065] In a third measurement, point C is plotted, a midpoint (2)
between point C and the previous midpoint (1) is obtained, and a
distance L2 between the midpoint (2) and the base point is
obtained. In a fourth measurement, point D is plotted, a midpoint
(3) between point D and the previous midpoint (2) is obtained and a
distance L3 between the midpoint (3) and the base point is
obtained.
[0066] In a fifth measurement, point E is plotted. Here, since
point E is out of a proper range, a midpoint and a distance are not
obtained and the previous midpoint (3) is retained. In a sixth
measurement, point F is plotted. Since point F is in the proper
range, a midpoint (4) between point F and the previous midpoint (3)
is obtained and a distance L4 between the midpoint (4) and the base
point is obtained.
[0067] A weighted average of the distances obtained in the
aforementioned manner is obtained, and if the weighted average is
less than or equal to a predetermined threshold and other
parameters described below satisfy conditions for a predetermined
period of time or longer, it is determined to have reached the
charge acceptance limit and the SOC of the secondary battery 20 at
such time is taken as a charge acceptance limit SOC. With the
aforementioned process, it can be determined whether or not the
secondary battery 20 has reached the charge acceptance limit, and
the charge acceptance limit SOC can be obtained.
[0068] Next, referring to FIG. 6, a detailed operation of the
present embodiment will be described. The flowchart shown in FIG. 6
is achieved by reading out and executing a program 15a from the
operation processing unit 11. This flowchart is executed at a
predetermined cycle (e.g., a cycle of a few tens of ms). When this
flow chart is started, the steps described below are performed.
[0069] Step S10: The operation processing unit 11 determines a base
point shown in FIG. 5. Specifically, as a base point, for example,
a point (14.5V, 0 A) may be taken as the base point. It is to be
noted that the secondary battery 20 experiences a drop in the
voltage at the charge acceptance limit in accordance with the
progress of degradation. As for the lead-acid battery, its life is
about two to three years and as it approaches the termination of
the life, a voltage at the charge acceptance limit decreases by
approximately a few tenths of V. By decreasing the base point by
approximately a few tenths of V (e.g., 0.1 to 0.5 V) at the largest
depending on (SOH: State of Health) which shows a state of the
battery, an optimum base point corresponding to the degradation of
the secondary battery 20 can be obtained. Also, rather than moving
the base point in accordance with the SOH, it is possible to move
the base point depending on a change (increase) in an internal
impedance of the secondary battery 20 or to move the base point
simply in accordance with an elapse of time. Also, the base point
may be moved by measuring a voltage before an engine start while
the voltage of the secondary battery 20 is stable, and estimating
the degradation based on the change (decrease) in the voltage.
[0070] Step S11: The operation processing unit 11 calculates an SOC
of the secondary battery 20. A method of calculating an SOC may be
a method in which, for example, a mathematical model of the
secondary battery 20 or the like is used, but any method may be
used.
[0071] Step S12: The operation processing unit 11 refers to an
output from the temperature sensor 14, determines whether or not
the temperature of the secondary battery 20 is within a proper
range, and if it is within the proper range (step S12: Yes),
proceeds to step S13 and, if not (step S12: No), proceeds to step
S30. Specifically, since the secondary battery 20 cannot make an
accurate measurement at a temperature of 0.degree. C. or below, if
an output from the temperature sensor 14 is higher than 0.degree.
C., the process proceed to step S13.
[0072] Step S13: The operation processing unit 11 refers to an
output from the voltage sensor 12, determines whether or not the
voltage of the secondary battery 20 is within a proper range, and
if it is determined to be within the proper range (step S13: Yes),
proceeds to step S14 and, if not (step S13: No), proceeds to step
S15. Specifically, if an output from the voltage sensor 12 is
greater than 12.5V, the process proceed to step S14.
[0073] Step S14: The operation processing unit 11 refers to an
output from the current sensor 13, determines whether or not the
electric current flowing in the secondary battery 20 is within a
proper range, and if it is determined to be within the proper range
(step S14: Yes), proceeds to step S17 and, if not (step S14: No),
proceeds to step S15. Specifically, if an output from the current
sensor 13 is greater than -15 A, the process proceed to step
S17.
[0074] Step S15: The operation processing unit 11 retains the
previous midpoint. In other words, if the voltage or the current is
out of the proper range, such as point E in FIG. 5, the previous
midpoint (3) is retained without setting a new midpoint. Thereby,
if the current and the voltage become proper in the next process,
for example, a midpoint (4) between point F and the retained
midpoint (3) is obtained and a distance L4 between the midpoint (4)
and the base point is obtained.
[0075] Step S16: The operation processing unit 11 sets a voltage
excess value which indicates that the voltage is not exceeding a
predetermined value (in this example, 12.5 V) is set to "0". This
voltage excess value is information expressed in one bit, and this
information is used in the calculation of step S23 described
below.
[0076] Step S17: The operation processing unit 11 determines
whether or not it is a first process, and if it is the first
process (step S17: Yes), proceeds to step S18, and if not, proceeds
to step S19. For example, in a case of point A in FIG. 5, it is the
first process and since the previous midpoint does not exist and
the distance cannot be obtained, the process proceeds to step
S18.
[0077] Step S18: The operation processing unit 11 sets the present
value to the midpoint. For example, in a case of point A in FIG. 5,
since point A which is a present value is set to the midpoint, a
midpoint (1) between point A taken as the midpoint and a new point
B is obtained in the next process.
[0078] Step S19: The operation processing unit 11 determines a
midpoint between two points (the previous midpoint and a plotted
point corresponding to the present measurement value).
Specifically, in the case of a second process indicated in FIG. 5,
since point A is set to the midpoint by the process of step S18 in
the first process, a midpoint (1) between point A and point B is
determined. Also, in a third process, a midpoint (2) between the
midpoint (1) and point C is determined.
[0079] Step S20: The operation processing unit 11 calculates a
distance of the base point from the midpoint. Specifically, in the
case of the midpoint (1), a distance L1 between the midpoint (1)
and the base point is calculated and in the case of a midpoint (2),
a distance L2 between the midpoint (2) and the base point is
calculated.
[0080] Step S21: The operation processing unit 11 calculates a
weighted average of the distances. Specifically, the calculation is
performed using the following equation.
[Equation 1]
Latest Average Distance=Previous Average
Distance.times.(1-W)+Latest Distance.times.W (1)
[0081] In the equation, W is a weight coefficient and more
specifically, W=0.002, for example. The results of calculation for
a case where a value of the weight coefficient W is varied will be
described later with reference to FIG. 8. A concrete calculation
method of the latest average distance will be described. In the
second process, the latest distance L1 is calculated but a previous
average distance does not exist at that time, and thus in such a
case, the latest average distance is obtained by the following
equation. In other words, the latest distance L1 becomes the latest
average distance.
[Equation 2]
Latest Average Distance=Latest Distance (2)
[0082] In the third process, since L2 is calculated as the latest
distance, the following calculation is carried out in accordance
with Equation (1), and the latest average distance is calculated:
Latest Average Distance=L1.times.(1-W)+L2.times.W. In a fourth
process, the previously calculated latest average distance is taken
as the previous average distance, and Latest Average
Distance=Previous Average Distance.times.(1-W)+L3.times.W is
calculated based on the newly calculated distance L3. In such a
manner, by using a weighted average, it will be not necessary to
store all distance data and it is possible to reduce a necessary
capacity of the storage unit 15.
[0083] Step S22: The operation processing unit 11 sets the voltage
excess value to "1". In other words, when proceeding to the process
of step S22, since the voltage has been determined to be within the
proper range in step S13, the voltage is exceeding a predetermined
value (in this embodiment, 12.5 V) and the voltage excess value is
set to "1".
[0084] Step S23: The operation processing unit 11 calculates a
voltage excess rate. Specifically, as shown in FIG. 7, the voltage
excess value which is set in step S16 or step S17 is substituted
into the MSB (Most Significant Bit) of a 10-bit register DT1. Here,
if the register DT1 already has data stored therein, a 1-bit right
shift of the register DT1 is carried out before storing new data.
When the register DT1 has become full (in a case where data is
stored in all of the ten bits), if there are eight or more bits set
to "1" among the ten bits, the MSB of a register DT2 is set to "1",
and if there are seven or less bits set to "1", the MSB of the
register DT2 is set to "0" and all the bits of the register DT1 is
cleared. Also, a 1-bit right shift of the register DT2 is carried
out. By repeating such an operation, when the register DT2 has
become full (in a case where data is stored in all of the ten
bits), if there are eight or more bits set to "1" among the ten
bits, the MSB of a register DT3 is set to "1" and if there are
seven or less bits set to "1", the MSB of the register DT3 is set
to "0" and all the bits of the register DT2 is cleared. Also, a
1-bit right shift of the register DT3 is carried out.
[0085] Step S24: The operation processing unit 11 determines
whether or not the voltage excess rate is within a predetermined
range, and if it is determined to be within the predetermined range
(step S24: Yes), proceeds to step S25, and if not (step S24: No),
proceeds to step S30. Specifically, in a case where eight or more
bits among the ten bits of the register DT3 shown in FIG. 7 is "1",
proceeds to step S25, and if there are seven or less bits, proceeds
to step S30.
[0086] Step S25: The operation processing unit 11 determines
whether or not the distance is within a predetermined range, and if
it is determined to be within the predetermined range (step S25:
Yes), proceeds to step S26, and if not (step S25: No), proceeds to
step S30. Specifically, in a case where a weighted average value of
the distances calculated using Equation 1 in the process of step
S21 is, for example, less than "2", it is determines as "Yes" and
the process proceeds to step S26, and if not, proceeds to step S30.
The determination value "2" is taken by way of example and other
values may be used.
[0087] Step S26: The operation processing unit 11 refers to an
output from the timer 16 and measures a condition satisfaction
duration. Specifically, a duration in which the voltage excess
value is within a predetermined range in step S24 and the distance
is within a predetermined range in step S25 is calculated by
referring to an output from the timer 16.
[0088] Step S27: The operation processing unit 11 determines
whether or not the condition satisfaction duration is within a
predetermined range, and if it determined to be within the
predetermined range (step S27: Yes), proceeds to step S28, and if
not (step S27: No), proceeds to step S31. Specifically, if the
condition satisfaction duration measured in step S26 is, for
example, 500 seconds or more, determines to be "Yes" and proceeds
to step S28 and, if not, proceeds to step S31.
[0089] Step S28: The operation processing unit 11 determines the
charge acceptance limit SOC. In other words, in case where the
conditions in steps S24 and S25 are satisfied continuously for a
certain period of time (500 seconds) or more, it is determined that
the secondary battery 20 has reached the charge acceptance limit,
and the SOC at such an instant (an SOC calculated in step S11) is
set to the charge acceptance limit SOC. Also, via an I/F 17, an
external device may be informed of the fact that the secondary
battery 20 has reached the charge acceptance limit and of the
charge acceptance limit SOC.
[0090] Step S29: The operation processing unit 11 calculates a
chargeable capacity and a dischargeable capacity based on the
charge acceptance limit SOC obtained in step S28. Specifically, as
shown in FIG. 12, when the charge acceptance limit SOC 51 is
determined, the chargeable capacity SOC1 and the dischargeable
capacity SOC2 are calculated based the relevant value.
[0091] Step S30: The operation processing unit 11 sets the
condition satisfaction duration to "0". Specifically, the process
proceeds to the process of step S30 in one of a case where the
temperature is determined as being not in the proper range in step
S12, a case where the voltage excess rate is determined as being
not in the proper range in step S24, and a case where the distance
is determined as being not in the proper range in step S25, and
since the condition is not satisfied continually in such a case,
the condition satisfaction duration is reset to "0".
[0092] Step S31: The operation processing unit 11 determines
whether or not the latest SOC is greater than the charge acceptance
limit SOC, and in a case where the following relationship holds:
Latest SOC>Charge Acceptance Limit SOC (step S31: Yes), proceeds
to step S32, and if not (step S31: No), proceeds to step S29. To be
more specific, in a case where, after the charge acceptance limit
SOC has been determined in step S28, an SOC having a value larger
than this was calculated in step S11, it is expected that the
charge acceptance limit SOC is not accurate, and thus it is
determined in step S31 whether such a situation has not occurred,
and if it has occurred, proceeds to step S32 and updates the charge
acceptance limit SOC.
[0093] Step S32: The operation processing unit 11 updates the
charge acceptance limit SOC with the latest SOC. Then, the process
proceeds to the process of step S29.
[0094] FIG. 8A is a diagram showing a transition over time of a
distance in a case where the aforementioned process was executed on
the secondary battery 20 near charge acceptance limit, and FIG. 8B
is a diagram showing a transition over time of a distance in a case
where the aforementioned process was executed on the secondary
battery 20 which is in a chargeable state. In these diagrams, a
horizontal axis represents time (seconds) and a vertical axis
represents distance. Also, each point represents distance
calculated in step S20, and a continuous line indicates an average
distance calculated in step S21. As shown in FIG. 8A, in a case
where it is near the charge acceptance limit, the continuous line
indicating the average distance has a smaller value as compared to
a chargeable case shown in FIG. 8B. Also, the average distance
shows a smooth transition without fluctuating up and down.
Accordingly, with the present embodiment, it is possible to
accurately determine the charge acceptance limit of the secondary
battery 20.
(F) Variant Embodiment
[0095] Each of the aforementioned embodiments is shown by way of
example and various other variant embodiments exist. For example,
in the aforementioned embodiment, 0.002 is uses as a value of the
weight coefficient W in Equation (1), but it is possible to use
other values. Generally, it is preferable that the value of the
weight coefficient W is not a particularly large value.
Specifically, in FIG. 8A, 0.002 is used as the value of the weight
coefficient W, but in FIG. 8C, 0.01 is used as the value of the
weight coefficient W. By comparing FIG. 8A and FIG. 8C, it can be
seen that, in a case where the value of the weight coefficient W is
0.01, the average distance shows a large vertical fluctuation.
Therefore, it is preferable to use a value of less than 0.01 as the
value of the weight coefficient W.
[0096] Further, in the aforementioned embodiments, a measurement
value was plotted on a current-voltage plane, a midpoint between
the plotted point and the previously obtained midpoint was
obtained, and a distance between the midpoint and this base point
was obtained, but other method may also be used. Specifically, a
distance between the plotted point of the measured value and the
base point may be obtained. Alternatively, a midpoint between the
plotted point of the measurement value and the plotted point of the
previous measurement value may be obtained and then a distance
between this midpoint and the base point may be obtained.
[0097] Also, in the aforementioned embodiment, a case where the
voltage and the current are not within the proper range was
excluded from the calculation in step S13 and step S14, but these
need not be excluded. Alternatively, in a case where they are not
within the proper range, these may be corrected to specified
values. Specifically, in a case where the voltage is 12.3 V, this
may be corrected to a specified value 12.5 V, or in a case where
the current is -16 A, this may be corrected to a specified value
-15 A. Here, such a correction may be performed in a case where
only one of the voltage value and the current value is out of the
proper range, and these measurement values may be excluded from the
calculation in a case where both are out of the proper ranges.
Alternatively, even in a case where both are out of the proper
ranges, these measurement values may both be corrected.
[0098] FIGS. 9A to 10D are diagrams showing measurement results
according to the aforementioned variant embodiments. In other
words, FIG. 9A is a measurement result for a case where a distance
between the plotted point of the measurement value and the base
point is obtained (e.g., a case where a distance between each of
the points A to F and the base point is obtained in FIG. 5); FIG.
9B is a measurement result for a case where a distance of a
midpoint between the plotted point of the measurement value and the
previous midpoint from the base point is obtained; FIG. 9C is a
measurement result for a case where a distance of a midpoint
between the plotted point of the measurement value and the previous
midpoint from the base point is obtained and where 12.5V or below
is excluded; and FIG. 9D is a measurement result for a case where a
distance of a midpoint between the plotted point of the measurement
value and the previous midpoint from the base point is obtained and
where 12.5V or below and -15 A or below are excluded (a case
similar to FIG. 6). FIGS. 10A to 10D show results indicating the
measurement result for a case where measurement was made under a
condition similar to those of FIGS. 9A to 9D with the scale of the
vertical axis being changed (the results indicated by changing a
range of distance 0 to 50 into a range of distance 0 to 10). Also,
the SOC at the time of these measurements is a value near 95. By
comparing FIG. 10A with FIG. 10B, it can be seen that the
fluctuation of the average distance in the vertical direction is
further suppressed when a midpoint is used. Also, by comparing FIG.
9C with FIG. 9D, it can be seen that points plotted at a distance
of greater than or equal to "10" are decreased by excluding -15 A
or less from the target of calculation. Although an effect of
excluding 12.5V or less from the target of calculation is not clear
from the comparison between FIGS. 9B and 9C and the comparison
between FIGS. 10B and 10C, it is possible to suppress the
fluctuation of the distance, specifically in a region where SOC is
low, by excluding 12.5 or below from the calculation.
[0099] In an embodiment shown in FIG. 6, a distance measurement is
not carried out in the first process and a distance measurement is
carried out in the second process onwards, however, for example, a
distance of point A from the base point shown in FIG. 5 may be
obtained and taken as a distance L0 in the first process, and
distances L1, L2, . . . may be calculated in a similar manner to
the aforementioned case in the second process and onwards. Of
course, in such a case, the latest average distance may be obtained
in accordance with Equation (2) in the process of step S21, and the
latest average distance may be obtained in accordance with Equation
(1) in the second process onwards.
[0100] Also, in the embodiment shown in FIG. 6, in a case where the
temperature condition is not satisfied in step S12, the condition
satisfaction duration is simply set to "0", but may be reset with
the weighted average value, for example. In such a case, when the
temperature condition is satisfied, by determining in step S17 that
it is the first process, the distance can be measured accurately
again.
[0101] Also, the proper ranges of the temperature, the voltage and
the current in steps S12 to S14 are described as fixed values, but
may be varied in accordance with aging or varied in accordance with
the usage environment. Similarly, the determined value of the
voltage excess rate, the determined value of the distance and the
condition satisfaction duration in steps S24, S25 and S27 may also
be variable values in accordance with the aging or usage
environment or the like.
[0102] Also, in each of the aforementioned embodiments, the
measurement values are plotted on the current-voltage plane, but
these need not be plotted as long as a distance between the base
point and one of the midpoint and the measured point can be
obtained. For example, the distance between these points can be
obtained by mathematical expressions.
* * * * *